FIG. 1 shows in a vertical sectional view, a first type of nuclear reactor of the pressurized water type from the prior art. Reference 1 designates, as in the other figures, the vessel of the reactor, while reference 2 designates the fuel rods which form the assembly called the core 50.
It is noted that an internal part for holding the core 50 called, in the subsequent patent application, an internal part or internal assembly referenced 10A. It is placed above the core 50 containing the fuel rods 2 and holds the fuel rods 50 into place, in the lower portion of the vessel 1, so that the vessel 1 does not move upwards under the effect of a very large water flux passing through the core 50 in an ascending movement. So this internal part or internal assembly 10A has a mechanical function.
FIG. 3 shows a boiling water type reactor according to the prior art. There again, the core 50 comprising the fuel rods 2 is placed below the internal part 10A inside the vessel 1. On the other hand, vapor dryers 36 are placed above the internal part 10A.
It is noted that in the reactors from the prior art, the internal part or the internal assembly 10A are not in contact with the outside of the vessel 2.
Stiff control rods 51 which are actuated from the outside of the vessel 1, are used in both of these nuclear reactor types, as in other types. In the case of the pressurized water reactor illustrated in FIG. 1, the control rods 51 pass through the vessel 1 through the upper lid and pass through the internal part 10A. Their control and guiding systems clutter up, inter alia, the upper portion of the lid of the vessel 1. In the case of the boiling water reactor illustrated in FIG. 3, the control rods 51 penetrate into the vessel 1 through its base and their guiding and control systems are placed under the base.
As a complement, in pressurized type reactors, it is also common to use a neutron absorber, i.e., boric acid, dissolved in the coolant flux in order to vary the reactivity homogeneously. On the other hand, varying the speed of the pumps is used for varying the reactivity in the boiling water type nuclear reactors to a lesser extent.
So it is seen that the installation required for controlling and regulating operation of the reactor's core 50 requires a large volume by virtue of the use of control rods 51, either above or below the core 50 and passing through the vessel 1, and mobilizes cumbersome chemical or mechanical complementary means.
A main object of the invention is therefore to find a remedy to this drawback by proposing a different method for controlling the nuclear reaction inside the vessel 1 of the reactor.